October 3, 2011

Talking Simplex on Ham Radio

Yesterday I made a bonehead mistake. Being a newbie in ham radios, this happens just about every time I touch a radio. Days before plans were made for an early breakfast with a fellow ham that was going to work a public service event with me.

I was to meet somewhere in Bristol, NH with this expert radio operator. Because neither of us knew what diners would be open, We decided to coordinate where to eat on simplex when we got close to one another. The plan was to be on 146.500 MHz.

You know what they say about best-laid plans, don't you? Well, I was able to broadcast and my friend heard me just fine. When he transmitted back to me, I could clearly see his signal via the S-meter on the screen of my Yaesu VX-7R. But there was no sound. Yes, I did have the volume up. He was deaf to me, if you get what I mean.

Because he was an experienced operator, he instantly knew what the problem was. But alas, he couldn't tell me how to fix my radio settings because I couldn't hear him.

It was so easy. I had my Tone Squelch setting set to On and had a preset tone set up.

You may not think that's a big deal, but the purpose of these Continuous Tone-Coded Squelch System (CTCSS) tones is to keep a radio quiet until it hears this simultaneous sub-audible tone during the voice transmission. These CTCSS tones are very low frequency audio tones, usually less than 300 Hz, that are overlaid on the radio frequency. These also are helpful in activating repeaters. But that's a subject for another day.

Since my radio was set to listen for such a tone, it did it's job and sat there oh so quietly.

It's also mandatory that you turn off the + / - repeater shift function on the radio. If you don't you'll be transmitting out at .600 on any simplex frequency in the 2-meter band you've chosen. This means my friend could not hear what I was transmitting, but I would have been able to hear what diner he was at.

Once my mentor and I caught up with one another on a local repeater and sat down for breakfast, we were able to get my radio working perfectly in less than 30 seconds. Once I turned off my tone squelch he pressed my talk button and it automatically made his radio chirp.

Additional Simplex Operating Tips:

Altitude is everything. When you operate in simplex mode, you want your radio waves to reach out as far as possible, especially if you're working with a low-wattage handheld (HT) radio like the Yaesu VX-7R. It only transmits at 5 watts. But 5 watts broadcasting from on top of a mountain can carry quite a distance indeed.

If you're blocked by terrain, trees, buildings, etc. simplex might only reach out a mile or so and even less.

Remember that propagation changes as the sun rises into the sky and excites the atmosphere. You may be able to work simplex early morning and evening with great success at a given distance, but have issues at high noon and midday.